1. Field of the Invention
The present invention relates to an electrolytic in-process dressing grinding apparatus suitable for grinding a planar or a spherical surface.
In general, grinding and polishing of a work such as one of an optical material into a spherical form is conducted by means of a tool such as a grinder. A process for processing a spherical surface, as an example of a known grinding operation, will be described with reference to FIG. 7.
FIG. 7 is a schematic illustration of a spherical surface grinding apparatus of the forced-machining type. This type of spherical surface grinding apparatus is disclosed, for example, in Japanese Patent Publication No. 61-33665, as well as in the lens/prism processing technique (Chuo Kagakusha).
Referring to FIG. 7, numeral 1 denotes a work, the surface of which is to be generated at a radius of curvature R.sub.o, and held on a work spindle unit by means of a collet chuck. The work spindle unit denoted by 3 is driven by a mechanism (not shown) so as to rotationally drive the work 1 while the work is cut in a direction a'. In order to permit adjustment of wall thickness of the work 1, the work spindle unit 3 is adjustable in the directions of arrows a. Numeral 4 denotes a grinder, while 5 denotes a grinder shaft. A coolant (not shown) is supplied between the work 1 and the grinder 4.
The operation of this grinding apparatus is as follows. It is assumed here that the work 1 is to be ground to have a spherical surface having a radius R.sub.0 of curvature as shown in FIG. 8, using the grinder 4 having a grinding radius d. To this end, the grinder shaft 5 is inclined at an angle .theta..sub.0 which is given by sin .theta..sub.0 =d/2R.sub.0, and is adjusted by means of a handle (not shown) in a direction b which is perpendicular to the grinder shaft such that the work diameter d coincides with the work axis at a point P, so that a spherical surface having the desired radius of curvature O.sub.0 P=R.sub.0 is generated. The symbol O.sub.0 represents the point where the work axis and the axis of the grinder cross each other at the angle .theta..sub.0, i.e., the center of the curvature of the spherical surface to be generated.
As a large number of works are processed, the grinder becomes dull due to clogging, causing problems such as reduction in the grinding power, coarsening of the ground surface of the work and burning.
In order to obviate these problems, it has been a common measure to conduct dressing of the grinder by a dressing tool between successive grinding cycles.
On the other hand, there are many current proposals in this field of technology: such as "Mirror-finish Grinding of Glass materials with Cast-iron Fiber-bond Abrasive" appearing in the first division of Gazzette of Lecture Meeting of Association of Precision Engineering, 1988 Autumn Session (Published on Oct. 3, 1988 by Corporation of the Association of P{precision Engineering), "Grinding of Silicone by Cast-iron Fiber-bond Abrasive" appearing in the third division of Gazzette of Lecture Meeting of Association of Precision Engineering, 1988 Autumn Session (Published on Oct. 5, 1988 by Corporation of the Association of P{precision Engineering), and "Electrolytic Dressing Mirror-finish Grinding of Glass with Electrodeposited Abrasive" appearing in the first division of Gazzette of Lecture Meeting of Association of Precision Engineering, 1989 Spring Session (Published on Mar. 22, 1989 by Corporation of the Association of P{precision Engineering).
FIG. 9(a) is a front elevational view, while FIG. 9(b) is a left side elevational view of a grinding/dressing system illustrative of the principle of dressing operation. In this system, a work 1 is disposed between a rotary table and a grinder which is mounted on a rotary grinder shaft 5. A power supply 12 is connected through a power feed brush 13 to the grinder so that the grinder forms a (+) electrode. A weak-electric coolant is applied between the grinder serving as the (+) electrode and an opposing (-) electrode so that the grinder is ground while being dressed. In this system, the position of the (-) electrode is always fixed with respect to the grinder shaft so as to maintain a constant gap between the (-) electrode and the grinding surface. The gap is adjusted so as to avoid interference between the grinder and the work.
In general, a grinder is progressively worn although the wearing rate varies according to conditions such as the type of the grinder, material of the work and the grinding conditions. The wear of the grinder causes the size of the gap between the grinder and the (-) electrode to be progressively increased so that the dressing effect is impaired.